Ceramic substrates are used in microelectronic packaging of semi-conductor chips. In semi-conductor chip packaging, it is known to provide input/output (I/O) pads on the surface of a ceramic substrate to which the leads of a semi-conductor chip are connected. I/O connector pins are typically brazed on the I/O pads of these ceramic substrates for establishing electrical connections to the next level of packaging. A variety of braze materials, such as pure silver and Cu--Ag brazes, have commonly been used to connect I/O connector pins to I/O pads which typically comprise refractory metals such as molybdenum, tungsten, or their alloys. It is known, however, that I/O connector pins are not easily brazed directly on surface pads of these refractory metal surface pads without first plating a thin layer of nickel (or other suitable nickel-containing material) as an adhesion layer on the refractory metal surface pad.
Plating of the surface pads requires the use of plating processes such as electroless plating techniques with materials such as Ni--B or Ni--P, or electrochemical plating techniques using electrodes to plate each feature with pure Ni. After plating the refractory metal surface pads, a diffusion anneal is performed to enhance adhesion between the surface pad and the plated material. Typically, diffusion annealing is conducted at 700.degree. C.-900.degree. C. to facilitate the formation of a good bond between the nickel-plated material and the refractory metal surface pad.
After performing these nickel-plating and diffusion annealing steps, the resultant nickel-plated surface of the refractory metal surface pad can then be brazed to I/O connection pins. Typically these I/O connection pins are made of a KOVAR.RTM. iron (52-57 wt %)-nickel (28-30 wt %)-cobalt (15-18 wt %) alloy or a KOVAR.RTM. alloy which has been nickel-plated. A eutectic copper-silver braze material having a composition of 28 wt %Cu-72 wt %Ag is commonly used to braze the I/O connector pin to the nickel-plated refractory metal surface pad.
The steps of nickel-plating and diffusion annealing required to bond the I/O connection pins to the I/O surface pads are expensive and time consuming. The braze alloy and brazing process of the present invention provides for the direct brazing of refractory metal surfaces thus eliminating the need for nickel-plating and diffusion-annealing steps required by brazing operations involving refractory metal features using conventional braze alloys.